1. Field of the Invention
A preferred embodiment relates to air springs for vehicle suspensions and preferably two-wheeled vehicle suspensions, such as the suspensions of bicycles, which are typically mounted between the chassis of the vehicle and a wheel. In particular, a preferred embodiment relates to an air spring, optionally combined with a shock absorber or other damper to form an integrated suspension unit, which permits instant selection between two different spring rate curves by simply rotating an external knob one-quarter turn.
2. Description of the Related Art
One advantage of air springs is the ability to change spring rate (“softer” or “stiffer”) simply by adjusting the internal air pressure. Such a method permits changing the spring rate curve of an air spring, and is available for essentially all air springs. On many air springs this is accomplished relatively easily by pressurizing or de-pressurizing the air spring with a hand pump and gauge, or by using an air pressure hose at an automobile service station (“gas station”). Most air springs are purposely designed with a standardized Schrader air valve (similar to those in automobile tires) to make this relatively easy and convenient.
As is known in the art, spring rate characteristics can also be changed by altering the initial air chamber volume. Increasing or decreasing initial air chamber volume softens or stiffens, respectively, the air spring curve.
Conventional prior-art air springs for bicycles and motorcycles have been known to provide features for altering air chamber volume. The most common method, used especially in air-sprung mountain bike front forks, is to increase or decrease air chamber volume by adding or removing hydraulic fluid (“changing the oil level”). In other cases, air spring suspension components have been provided with solid, light-weight, “volume plugs”. The air spring is opened and the “volume plugs” are added or removed from the air chamber. Both methods, of course, generally require depressurization and opening of the hydraulic unit and/or the air spring.
Another feature known in the art for altering the air chamber volume on certain bicycle and motorcycle air springs has been an adjustable-position threaded cap closing off the air chamber. Threading this cap in or out, which can require a fair amount of torque to overcome frictional forces resulting from the internal pressure, changes the air chamber volume. For example, U.S. Pat. No. 5,346,236 teaches this for a bicycle front fork. Also known in the art is a threaded-cap adjustable-volume external air reservoir which can be added to a basic shock absorber or fork air spring. Changes of this type can typically be accomplished faster than adding or removing hydraulic fluid, and may be accomplished in about 1 minute.
Motorcycles having air suspension with an on-board pressurization system including an on-board air compressor to monitor and regulate air pressure on demand, are also known in the art.
There is a need in bicycles and motorcycles which incorporate air spring suspension for a quick, easy way to alter the air spring curve “on-the-fly”. All the prior-art methods noted above suffer from various limitations, including time and effort required, weight, bulk, complexity, and cost.